Conventionally, as a refrigerant for automobile air conditioners or the like, 1,1,1,2-tetrafluoroethane (HFC-134a) has been widely used. However, HFC-134a has a high global warming potential (GWP) of 1430, and hence its use has become restricted due to movement toward restricting refrigerant having high GWP in recent years, for example, prohibiting use of a refrigerant with GWP of 150 or more in new models of automobiles in EU from the year 2011, and the like. Here, in this description, for halogenated hydrocarbons, an abbreviation of a chemical compound will be described in parentheses after a chemical compound name, but in this description such an abbreviation is also used instead of a chemical compound name as necessary.
Then, as an alternative refrigerant for HFC-134a, use of 2,3,3,3-tetrafluoropropene (HFO-1234yf) with a quite low GWP of 4 is becoming popular. In manufacturing HFO-1234yf, alkaline washing and water washing are performed for removing acids used or generated such as hydrofluoric acid, hydrochloric acid, and the like, and thus crude liquid often contains water besides fluorine-based low-molecular organic impurities of intermediates, by-products, non-reacted raw materials, and the like.
When such crude liquid of HFO-1234yf is purified by distillation, HFO-1234yf and water form an azeotrope mixture, and thus water contained in the crude liquid condenses in a column-top reflux line, and water in an obtained product increases. Thus, Patent Reference 1 (WO2010/024366) describes a manufacturing method of HFO-1234yf which makes an HFO-1234yf product with less water from a bottom product obtained from a bottom part of a distillation column.
However, among the fluorine based low-molecular organic impurities contained in the HFO-134yf crude liquid, there are many organic impurities having higher boiling point than that of HFO-1234yf, and such many organic impurities are mixed into the bottom product obtained from the bottom part of the distillation column. Thus, it has been necessary to further remove the organic impurities in another process.